The Defense Department released the final findings of an investigation into Project 112 and Project SHAD, which were conducted from 1962 to 1973 to test the combat capabilities of biological and chemical agents and ways to protect U.S. troops from such attacks.

Monday's report raised the number of U.S. troops identified as having been present for one or more of the tests to 5,842, many of whom were not informed of their participation.

Some included releases of deadly biological and chemical agents, but troops were protected in those cases, said Dr. Michael Kilpatrick, deputy director of the Defense Department's Deployment Health Support Directorate.

Rep. Mike Thompson, D-Calif., and several of his colleagues said it would be premature to close the book on the investigations and asked Rumsfeld to continue the inquiry.

"Veterans who may have been exposed during these tests deserve to know all the facts," Thompson said. "The Department of Defense's decision to close its investigation may unfairly deny them that right."

To date, the Veterans Administration has had 260 claims filed by service members who believe their ailments are related to their presence at the test sites, although such cases are difficult to prove, said Kilpatrick.

Project 112 and Project SHAD were developed in 1961 to study the combat uses of biological and chemical weapons and methods to protect American troops from such attacks. Initially it was believed that only simulated agents were used, but last year the Defense Department admitted for the first time that some of the tests used real chemical or biological weapons.

Most of the tests made public Monday used the benign bacteria bacillus globigii to simulate how biological weapons agents would spread through the hold of a ship.

One test, called "Blue Tango," entailed spraying two types of bacteria, including E. coli, in a rain forest in Hawaii in 1968 to gauge how the bacteria would linger in the vegetation.

Another, "Folded Arrow," involved spraying bacillus globigii from a submarine over part of Oahu, Hawaii, and over several boats off the coast in 1968 to gauge how Venezuelan equine encephalitis would be carried by wind.

"It bespeaks the time, the early '60s, when we were in the Cold War, and we were concerned that Russia and perhaps China had chemical and biological capabilities that could be used against American troops and against us in the homeland," Kilpatrick said.

The United States scrapped its biological weapons program in the late 1960s and agreed in a 1997 treaty to destroy all its chemical weapons.

None of the tests were conducted to gauge the human response to chemical or biological weapons, said Kilpatrick. In each test, military personnel were protected from the agents by shelter, protective clothing or vaccinations.

Even if none of the military personnel was harmed, there remain ethical questions of conducting tests on unwitting soldiers, said Steven Aftergood, an expert on government secrecy with the Federation of American Scientists.

"If there were no illnesses caused, which I think is still an open question, then it is a matter of luck, and one of the reasons government accountability and transparency are so important is to prevent initiatives of this kind," he said.

The inquiry began in three years ago, after several Navy veterans reported health problems they believed might be caused by their involvement in the tests. Research into the classified project found more tests and many more veterans present, expanding the scope of the investigation.

Kilpatrick said the VA was seeking to notify the 5,842 veterans who were present for the tests.

Several House members are asking Defense Secretary Donald H. Rumsfeld to keep alive the Pentagon's investigation into 50 chemical and biological weapons tests in the 1960s that involved 5,842 military personnel.